They had been due to visit the city last month but were diverted to track a Russian aircraft carrier through the North Sea and on to the Mediterranean.

Spanish Officer, Rear Admiral Jose Enrique Delgado, who commands the group, played down any perceived threat.

He said: "We were tasked to monitor the Russian task group movements from the northern seas into the Mediterranean. So that is what we have been doing.

"There was no threat at all. We were just conducting normal maritime surveillance which is a routine activity. It was not challenging, it was just monitoring their activities.

"It was nothing special."

The ships - from the Standing Nato Maritime Group One (SNMG1) include the Belfast-affiliated HMS Duncan as well as vessels from Spain, Portugal and Germany - are manned by more than 700 sailors.

They will be at Gotto Dock in Belfast until Monday but will not be open to the public because of security issues.

"All our sailors are delighted to pull into this port. All we know about this port is good news," said the senior officer.

"We normally open the ships to the public but due to security issues of the commercial port we are in we have been advised that it is not possible because of security and safety reasons."

The ships are ESPS Almirante Juan de Borbon, a Spanish frigate; NRP Alvares Cabral, a Portuguese frigate; FGS Ludwigshafen and FGS Rhon, German naval corvette and support ship; and HMS Duncan, a Royal Navy Type 45 Destroyer.

They have recently completed a major exercise off the coast of Scotland.

Rear Admiral Delgado said: "Our main task is to be ready to provide Nato with a permanent maritime capability. To do that we have to do training and exercises and that will take a big part of our activity across the year.

"We have to train and conduct high level exercises to be operationally ready to deploy in a crisis or any task that Nato decides that we should go."

Meanwhile, HMS Duncan previously visited Belfast in July 2014, but has since been active in the Mediterranean and Middle East, as well as training in UK and northern waters.

Although part of the Nato group, crew members will take time to catch up with affiliations in Belfast including at the City Hall, the Northern Ireland Children's Hospice, Sea Cadets and the Royal Naval Reserve unit HMS Hibernia.

Veterans and emergency services will also be invited on board.

Commanding Officer Charles Guy said: "It has been a couple of years since the ship has been in Belfast so we will do as much as we can.

"We have got community groups and cadets coming on board in reasonably large numbers. We have also got HMS Hibernia which is near Belfast coming on board as well.

"We have also got some charity money which the ship's company collected last year when it was on a deployment to the Arabian Gulf last year to present to the Northern Ireland Children's Hospice as well."

The fleet of war ships is expected to sail out of Belfast Port on Monday.